Japanese Patent Application Publication No. 2008-53648 (Patent Document 1) discloses a semiconductor device in which a diode region and an IGBT region are formed on a same semiconductor substrate. In the diode region, an n-type cathode layer is formed on the back side of the semiconductor substrate, and in the IGBT region, a p-type collector layer is formed on a back side of the semiconductor substrate. The cathode layer and the collector layer come into contact with each other, and the boundary exists in a boundary region between the diode region and the IGBT region.